In sewing machines generally, it has been known that at the sewing termination point of one of a plurality of continuous sewn portions of a workpiece or at the termination point of the sewing operation for all the sewn portions, the sewing machine must be precisely stopped so that the seam or seams will not deviate from the end of the workpiece.
Hithertofore, a variety of methods for stopping sewing machines in such a manner have been attempted.
According to the first method, when a seam is formed to finish at a position adjacent to an end edge of a workpiece where the sewing operation is scheduled to terminate, the operator reduces the force applied to the pedal so that the sewing machine is driven at a low speed, stops the machine when the seam reaches the predetermined sewing termination point and then depresses the pedal again to effect thread cutting. However, this method requires that the operator controls the pedal with great care. According to the second method, a workpiece detector means utilizing light is disposed upstream of the sewing zone in the sewing machine in the workpiece feed direction and the sewing machine stops automatically as the trailing end edge of a workpiece passes by the workpiece detector means independently of the pedal control. However, this method involves the drawback that when a seam is formed along an end edge of a workpiece having a complicated configuration such as a wave or concavo-convex shape, for example, the workpiece end edge tended to deviate at concavo-convex corners thereof from its proper position with respect to the workpiece detector means whereby the sewing machine is inadvertently stopped. This results in a substantial reduction of operation efficiency.
According to the third method, when a workpiece detector means detects the trailing end edge of a workpiece, the sewing machine stops and a thread cutter means is operated. However, this method involves the drawback that when a seam is formed along an end edge of a piece of cloth having a complicated configuration or of a piece of cloth having a square configuration such as a neck, collar, sleeve or cuff, each time the workpiece end edge deviated at a corner of square or concavo-convex configuration from its proper position with respect to the workpiece detector means, the sewing machine stops and the thread cutter means is operated, thereby making it impossible to form a continuous seam along the workpiece end edge and impairing the quality of a sewn product.